Semiconductor devices require radiation of heat produced in semiconductor elements in order to control the operating temperature to within a predetermined range. To address this, a known semiconductor device includes a metal base plate with high thermal conductivity disposed on the back of a ceramic substrate to which semiconductor elements are bonded (see, for example, PTL 1).
In such a semiconductor device, heat produced in any semiconductor element is conducted to the metal base plate through an insulating layer such as the ceramic substrate and an organic insulating sheet and is radiated through a cooler connected to the metal base plate to improve the heat radiation. With an increasingly higher density of integrated semiconductor elements in recent years, however, the heat radiation needs to be further improved.
In addition, the use of an organic insulating sheet as the insulating layer between the semiconductor element and the metal base plate has been disclosed. The organic insulating sheet includes inorganic powder (filler) with high thermal conductivity mixed in order to increase thermal conductivity (see, for example, PTL 2).